Occurrence of sialidase activity in two distinct and highly homogeneous populations of lysosomes prepared from the brain of developing mouse

Light and heavy lysosomes of mouse forebrain were separated from each other by centrifugation on a Percoll gradient. Light lysosomes were then freed from mitochondria and membranes by sucrose density gradient centrifugation and further purified by floatation-centrifugation on a sucrose gradient. The final preparations of light and heavy lysosomes, fairly homogenous, carried sinlidase activity, assayed on MU-NeuAc. The optimal pH was 4.0 and 4.2, the apparent K_m value 2.8 × 10^-3 M and 4.2 × 10^-3 M and the apparent V_max value 0.11 and 0.47 mU mg^-1 protein, for the light and heavy lysosome sialidase, respectively. From 4 days to adulthood the specific activity of the light and heavy lysosome sialidase increased 3-fold and 1.7-fold, respectively.